OPTICAL SENSOR DEVICE

• US 20140070077A1
• Filed: 11/19/2013
• Published: 03/13/2014
• Est. Priority Date: 05/20/2011
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: TSUCHIMOTO, HIROFUMI, Shimuta, Toru
• Granted Patent: US 9,360,365 B2
• Time in Patent Office: Days
• US Class Current: 250/214.A
• CPC Class Codes: A61B 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6829 Foot or ankle
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/444 Compensating; Calibrating, e.g. dark current, temperature drift, noise reduction or baseline correction; Adjusting
• CPC Class Codes: G01J 3/427 Dual wavelengths spectrometry
• CPC Class Codes: G01N 21/256 Arrangements using two alternating lights and one detector
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence

Abstract

An optical sensor device includes a light emitter for emitting, to a living body, lights having two wavelengths and blinking at a predetermined frequency, and a light receiver for receiving the lights from the living body. The light receiver outputs first and second detection signals corresponding to the respective wavelengths. A filter circuit extracts, from the first and second detection signals, modulation signals that are obtained with amplitude modulation of signals of the predetermined frequency. The modulation signals are amplified by a post-amplifier and are taken into an arithmetic processing unit after being converted to digital signals by an AD converter. The arithmetic processing unit calculates DC components and AC components of the first and second detection signals by employing the modulation signals converted the digital signals.

Claims

1. An optical sensor device comprising:

a light emitter configured to periodically emit light at a predetermined frequency toward a measurement target;

a light receiver configured to detect at least one of reflected light and diffused light from the measurement target, and to output an electrical signal based on the detected light;

a filter circuit configured to modulate the electrical signal at the predetermined frequency and to output a modulation signal;

an amplifier configured to amplify the modulation signal;

an AD converter configured to convert the modulation signal to a digital signal; and

an arithmetic processing unit coupled to the AD converter and configured to calculate a DC component and an AC component of the electrical signal based on the digital signal.

2. The optical sensor device according to claim 1, wherein the filter circuit comprises a frequency band that corresponds to a portion of the electrical signal.

3. The optical sensor device according to claim 1, wherein the light emitter comprises:

a first light emitting element configured to emit light in a first wavelength band at the predetermined frequency; and

a second light emitting element configured to emit light in a second wavelength band at the predetermined frequency, the second wavelength band being different than the first wavelength band.

4. The optical sensor device according to claim 3, wherein the first and second light emitting elements are configured to concurrently emit light at the predetermined frequency.

5. The optical sensor device according to claim 3, wherein the first and second light emitting elements are configured to alternately emit light at the predetermined frequency.

6. The optical sensor device according to claim 3, wherein the light receiver is further configured to detect light in both the first and second wavelength bands and to output a first electrical signal and a second electrical signal corresponding to light emitted from the first and second light emitting elements, respectively.

7. The optical sensor device according to claim 6, wherein the arithmetic processing unit is further configured to calculate an absorbance ratio of the measurement target based on a ratio of a first ratio between an amplitude of a first AC component and a first DC component calculated from the first electrical signal, to a second ratio between an amplitude of a second AC component and a second DC component calculated from the second electrical signal.

8. The optical sensor device according to claim 1, wherein the arithmetic processing unit is configured to calculate the DC component of the electrical signal by determining a time-average value of the modulation signal, and to calculate the AC component of the electrical signal by excluding the DC component from the modulation signal.

9. The optical sensor device according to claim 8, wherein the arithmetic processing unit is further configured to:

calculate the DC component by calculating a total DC component based on both extraneous light noise and the detected light by employing a signal contained in the modulation signal and obtained during an on-period of the light emitter;

calculate a DC component attributable to the extraneous light noise by employing a signal contained in the modulation signal and obtained during an off-period of the light emitter; and

calculate the DC component attributable to the detected light by excluding the DC component attributable to the extraneous light noise from the calculated total DC component.

10. The optical sensor device according to claim 1, further comprising:

a separation circuit including the filter circuit and configured to separate the modulation signal and the DC component of the electrical signal,

wherein the AD converter is further configured to convert the DC component of the electrical signal to a DC component digital signal, and

wherein the arithmetic processing unit is further configured to convert the modulation signal and the DC component digital signal based on an amplification factor of the amplifier, such that an amplitude ratio between the modulation signal and the DC component digital signal reaches a state before the amplification by the amplifier, and to calculate the AC component of the electrical signal based on the modulation signal.

11. The optical sensor device according to claim 10, wherein the arithmetic processing unit is further configured to calculate the DC component attributable to extraneous light noise based on a signal contained in the DC component of the electrical signal and obtained during an off-period of the light emitter.

12. An optical sensor device comprising:

a light emitter configured to emit light toward a measurement target;

a light receiver configured to detect at least one of reflected light and diffused light from the measurement target, and output an electrical signal based on the detected light;

a separation circuit configured to separate the electrical signal into a DC component and an AC component;

an amplification circuit configured to amplify the DC component and the AC component, at first and second amplification factors, respectively;

an AD converter configured to convert the DC component and the AC component to first and second digital signals, respectively; and

an arithmetic processing unit configured to restore the DC component and the AC component of the electrical signal by converting the DC component and the AC component output as the first and second digital signals such that an amplitude ratio between the DC component and the AC component output as the digital signals obtains a state before the amplification by the amplification circuit.

13. An optical sensing method comprising:

emitting light, by a light emitter, at a predetermined frequency towards a measurement target;

detecting, by a light receiver, at least one of reflected light and diffused light from the measurement target;

outputting, by the light receiver, an electrical signal based on the detected light;

modulating, by a filter circuit, the electrical signal at the predetermined frequency;

outputting, by the filter circuit, a modulation signal corresponding to the electrical signal;

amplifying, by an amplifier, the modulation signal;

converting, by an AD converter, the amplified modulation signal to a digital signal; and

calculating, by a processor, a DC component and an AC component of the electrical signal based on the digital signal.

14. The optical sensing method according to claim 13, further comprising:

calculating, by the processor, the DC component of the electrical signal by determining a time-average value of the modulation signal; and

calculating, by the processor, the AC component of the electrical signal by excluding the DC component from the modulation signal.

15. The optical sensing method according to claim 14, further comprising:

calculating, by the processor, a total DC component based on both extraneous light noise and the detected light by employing a signal contained in the modulation signal and obtained during an on-period of the light emitter;

calculating, by the processor, a DC component attributable to the extraneous light noise by employing a signal contained in the modulation signal and obtained during an off-period of the light emitter; and

calculating, by the processor, the DC component attributable to the detected light by excluding the DC component attributable to the extraneous light noise from the calculate total DC component.

16. The optical sensing method according to claim 13, further comprising:

separating, by a separation circuit including the filter circuit, the modulation signal and the DC component of the electrical signal;

converting, by the AD converter, the DC component of the electrical signal to a DC component digital signal;

converting, by the processor, the modulation signal and the DC component digital signal based on an amplification factor of the amplifier, such that an amplitude ratio between the modulation signal and the DC component digital signal reaches a state before the amplification by the amplifier; and

calculating, by the processor, the AC component of the electrical signal based on the modulation signal.

17. The optical sensing method according to claim 16, further comprising calculating, by the processor, the DC component attributable to extraneous light noise based on a signal contained in the DC component of the electrical signal and obtained during an off-period of the light emitter.

18. The optical sensing method according to claim 13,

wherein the step of emitting light further comprises:

emitting, by a first light emitting element of the light emitter, light in a first wavelength band at a predetermined frequency towards the measurement target; and

emitting, by a second light emitting element of the light emitter, light in a second wavelength band at the predetermined frequency towards the measurement target,

wherein the step of outputting the electrical signal comprises outputting, by the light receiver, first and second electrical signal based on the detected light in the first and second wavelength bands, respectively, and

wherein the step of calculating the DC component and AC component comprises;

calculating, by the processor, a first DC component and a first AC component of the first electrical signal; and

calculating, by the processor, a second DC component and a second AC component of the second electrical signal.

19. The optical sensing method according to claim 18, wherein the steps of emitting light in the first and second wavelength bands is performed either concurrently at the predetermined frequency or alternately at the predetermined frequency.

20. The optical sensing method according to claim 18, further comprising calculating, by the processor, an absorbance ratio of the measurement target based on a ratio of a first ratio between an amplitude of the first AC component and the first DC component, to a second ratio between an amplitude of the second AC component and the second DC component.